Apparatus

The apparatus shown in Fig comprises a gas burette of the type described under assay of nitrous oxide.in which tube B is connected to a gas pipette comprising two bulbs of suitable size.

Method

Charge the pipette with the reagents specified in the monograph. With the two-way tap open to tube B, draw the solution just to the level of the tap by moving the mercury reservoir. Open the two-way tap to tube A, completely fill the burette and tube A with mercury and close the two-way tap.

Connect a rubber tube to the exit valve of the cylinder of the gas under examination through a suitable pressure reducing device and pass a current of the gas through the tube for 1 minute. Whilst the gas is still flowing, connect the rubber tube to tube

A, immediately open the two-way tap to tube A, allow the specified quantity of the gas to enter the burette by lowering the mercury reservoir and close the two-way tap. Increase the pressure of the gas by raising the mercury reservoir, open the two-way tap to tube B and transfer all the gas to the pipette.

Close the tap and gently shake the pipette. After 15 minutes, when most of the gas has been absorbed by the liquid, draw the residual gas back into the burette and repeat the procedure beginning at the words "Increase the pressure of the gas .." until the volume of residual gas is constant. Measure the volume of the residual gas in the burette.